The present invention relates to a semiconductor device and a manufacturing method thereof. More specifically, the present invention relates to a semiconductor device having a wiring layer whose main component is copper and which is suited for micro-processing such as processing in 0.35 or 0.25 micron for example and a manufacturing method thereof.
It is desirable to reduce electrical resistance of a wiring layer used in a semiconductor device when it is to be processed below 0.35 micron (hereinafter referred to as micro-processing). While a wiring layer made of aluminum is used in processing over 0.35 micron, there has been known awiring layer made of copper or mainly made of copper as a wiring material of the next generation which replaces aluminum. However, although electrical resistance of copper is lower than that of aluminum, it is hard to process and can be patterned normally only in high temperature. Accordingly, it is difficult to pattern it by using a resist as a mask like aluminum.
In general, the wiring layer whose main component is copper is formed as follows. That is, a wiring groove is formed on a part of an insulating layer such as SiO.sub.2 formed on the surface of a silicon substrate at first. Then, the wiring layer is formed in the wiring groove by forming a metallic compound film whose main component is copper on the silicon substrate and by processing (polishing) the metallic compound film by a damascene method by means of chemical mechanical polishing (CMP) or the like. Because copper is apt to diffuse on the surface of the silicon substrate and into SiO.sub.2 as compared to aluminum, a barrier layer is used in order to prevent the diffusion. Presently, TiN, WN, TaN and the like are known to be used as a material for forming the barrier layer.
Because the capability of TiN and WN and the like to stop the diffusion of a copper wiring layer is poor, the barrier layer has to be thickened. Therefore, barriers SbTin, WN and the like are not suited for micro-processing. Because an aspect ratio of the wiring groove increases in micro-processing, coverage around an opening wiring groove of the forming a barrier is inferior, and thus it is hard to form the wiring layer.
Further, even if the barrier layer may be formed by TiN, WN and the like, the electrical resistance of the wiring increases even through low resistance copper is used for the wiring layer because the electrical resistance of the barrier layer is higher than that of copper.
Although it is possible to form a thin film of TaN, the specific resistance of TaN is relatively high, e.g., 560 .mu..OMEGA.cm. The finer the micro-processing, the greater the resistance becomes when TaN is used in the wiring groove.
In this area of thin film technology, Japanese Patent Laid-Open publication No. Hei. 5(1993)-291560 describes a compound of titanium (in part or the wholly amorphous) and nitrogen used as the barrier layer. In order to make the barrier layer amorphous, TiN is formed on a silicon substrate by reactive ion beam sputtering, and nitrogen ion beam is irradiated to amorphous TiN. More specifically, TiN is formed by continuously varying an input angle of the nitrogen ion to be irradiated between 10 and 90.degree. with respect to the surface of the silicon substrate and by turning the substrate. Nitrogen must be injected because the TiN layer will not become amorphous just by sputtering. The extra step of injecting nitrogen increases cost. Further, because the aspect ratio of the wiring groove increases in micro-processing, it becomes difficult to inject nitrogen into shadow parts of the wiring groove. Accordingly, it is not suitable to use this barrier layer for micro-processing.
Although aluminum is used in the technology disclosed in this publication, its fusion point is 660.4.degree. C. (the melting point of copper is 1083.4.degree. C.) and heat treatment can be performed only in low temperatures below that melting point after forming the wiring layer. This causes a problem in implementing heat treatments in forming a protection film, multi-layered wiring and the like.
A wiring layer made of aluminum and having a barrier layer made of nitride or carbide whose main component is Ta is described in Japanese Patent Laid-Open publication Nos. Hei. 7(1995)-130849 and Hei. 1(1989)-268025. The thickness of the barrier layer described in those publications is about 100 nm, and therefore, has similar problems with those described above.